Chapter 10: Methods for the Microbiological Examination of Foods

To study the presence and activity of micro-organisms in foods for investigative purposes or to determine its microbiological quality, it is frequently necessary to quantify and identify a food’s microflora. A large number of techniques are available to achieve this. A direct microscopic count can sometimes be used, but cultural methods where the microbe’s ability to self-amplify and produce a visible signal, usually in the form of a colony on an agar plate or turbidity in a broth, are still widely used. The principles of enumeration methods and the use of selective and differential media are described along with alternatives such as dye reduction test, ATP determination and conductance/impedance monitoring. A range of identification techniques have been developed from phenotypic methods, based largely on biochemical tests, to serological testing and methods, based on genotype and often based on the use of polymerase chain reaction (PCR). Most recently, the advances of next-generation sequencing have facilitated the development and use of whole-genome sequencing which is being increasingly applied, particularly in the study, monitoring and epidemiology of foodborne pathogens.